Android kotlin ViewBinding kotlin.UninitializedPropertyAccessException: lateinit 属性绑定尚未初始化

Question

So I want to access a view in a fragment from another fragment. Here I use viewBinding in both fragment. This is what the layout looks like where the View I want to access from other fragment is:

fragment_dashboard.xml

  <layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <androidx.drawerlayout.widget.DrawerLayout
        android:id="@+id/drawerLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <FrameLayout
                android:layout_width="match_parent"
                android:layout_height="0dp"
                android:layout_weight="1"
                android:id="@+id/content"/>

            <com.google.android.material.bottomnavigation.BottomNavigationView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom"
                android:id="@+id/bottomNavigationView"
                android:background="?android:attr/windowBackground"
                app:itemBackground="@color/buttonColor"
                app:itemIconTint="@drawable/bottom_navigation_selector"
                app:itemTextColor="@drawable/bottom_navigation_selector"
                app:menu="@menu/bottom_navigation_menu"/>


        </LinearLayout>

        <com.google.android.material.navigation.NavigationView
            android:id="@+id/navView"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            app:itemTextColor="@color/buyItemButtonColor"
            android:fitsSystemWindows="true"
            app:headerLayout="@layout/nav_header"
            app:menu="@menu/nav_drawer_menu" />


    </androidx.drawerlayout.widget.DrawerLayout>

</layout>

This is what fragment_dashboard.xml 's Fragment snippet code:

DashboardFragment.kt

class DashboardFragment : Fragment(), NavigationView.OnNavigationItemSelectedListener {

lateinit var binding: FragmentDashboardBinding
var currentSelectedMenu by Delegates.notNull<Int>()

lateinit var username: String
lateinit var memberId: String

private val onNavigateItemListener = BottomNavigationView.OnNavigationItemSelectedListener{ item ->
    ...
}


private fun addFragment(fragment: Fragment) {
    fragmentManager
        ?.beginTransaction()
        ?.setCustomAnimations(R.anim.design_bottom_sheet_slide_in, R.anim.design_bottom_sheet_slide_out)
        ?.replace(R.id.content, fragment, fragment.javaClass.simpleName)
        ?.commit()
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {

    binding = DataBindingUtil.inflate(
        inflater,
        R.layout.fragment_dashboard, container, false
    )

    val args = arguments?.let {
        DashboardFragmentArgs.fromBundle(
            it
        )
    }


    if (args != null) {
        binding.navView.setNavigationItemSelectedListener(this)
    }

    binding.bottomNavigationView.setOnNavigationItemSelectedListener(onNavigateItemListener)

    val fragment = HomeFragment.newInstance(memberId, username)
    addFragment(fragment)

    // Inflate the layout for this fragment
    return binding.root
}


fun openNavDrawer(){
    binding.drawerLayout.openDrawer(GravityCompat.START)
}

The function openNavDrawer() will be executed from another fragment ( HomeFragment.kt ). Here's the snippet code from HomeFragment.kt

HomeFragment.kt

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {

    binding = DataBindingUtil.inflate(inflater, R.layout.fragment_home, container, false)

    ...

    binding.navigationDrawerTrigger.setOnClickListener {
        DashboardFragment().openNavDrawer()
    }

}

But when executed, it returned:

kotlin.UninitializedPropertyAccessException: lateinit property binding has not been initialized
    at com.example.centuryememberproject.dashboard.DashboardFragment.openNavDrawer(DashboardFragment.kt:154)
    at com.example.bottomnavigationexample.HomeFragment$onCreateView$1.onClick(HomeFragment.kt:83)
    at android.view.View.performClick(View.java:6719)
    at android.view.View.performClickInternal(View.java:6677)
    at android.view.View.access$3400(View.java:797)
    at android.view.View$PerformClick.run(View.java:26475)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:226)
    at android.app.ActivityThread.main(ActivityThread.java:7212)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:576)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:956)

Did I miss something? Or maybe the variable binding from in the DashboardFragment.kt should moved elsewhere? If there's any detail I miss to point out, just let me know !

Answer 1

• Caused

When You click in HomeFragment with DashboardFragment().openNavDrawer() ,

binding.navigationDrawerTrigger.setOnClickListener {
        DashboardFragment().openNavDrawer()
    }

it means you call openNavDrawer() with a new fragment instance of DashboardFragment , (the new one)

not the original fragment . (the original one)

---

• Why

it has not been initialized?

Because it (the new one) did not managed by your FragmentManager and show on screen so that will not do createView()

(although you should not do this with DashboardFragment())

---

• What Should you do

You should use the original dashboard fragment to do what you want to do.

Such as:

1. Pass dashboard reference into home
2. find the dashboard fragment by your fragmentManager in home

then home can interact with dashboard

binding.navigationDrawerTrigger.setOnClickListener {
        the_origin_dashboard_fragment.openNavDrawer()
    }